Why do so few plants grow on the rainforest floor?

Due to the light in the bottom of the forest (covered by tall trees) the light does not give photosythesis to the plants so thats why the grass, moss, etc plants can't grow without light so thats why the bottom of the forest has scarce amount of pkants or organism down there but like noctural animals can live very well in dark areas on the bottom levels of the forest.